Troubleshooting UI crashes

There are a number of reasons why the Views UI may crash; the most common state or result of a crash is either a white screen (everyone's favorite WSOD), or a screen of what looks like garbage text. This is generally a javascript crash of some fashion.
To get the most timely and accurate help in the issue queue, please try to gather this information:
Check your javascript console. In Firefox, you can hit ctrl-shift-j or use firebug. Copy this information into the issue, or attach it as a text file. Really - this is the single biggest thing you can do to help figure out where the crash is coming from.

JSON prepends data with jQuery, causing editing and preview problems.

This section originally stems from this issue.
Some modules may add PHP improperly, disrupting normal jQuery operation. Errors may look like
session_module_name("files"); ?>{ "default": "default" }
This can also be a server configuration issue. In one case, this was solved by commenting out
auto_prepend_file = c:\wamp\www\php.ini.prepend
in the php.ini.
Another page to look at is the drupal.org page on White screens